Almost all of the air we breathe and liquids we drink are processed through fluid exchangers that heat/cool, process, and/or distribute as required. Such fluid exchangers include the HVAC system for building air, water delivery systems, or fluid dispensing equipment used in food processing. Processing the fluids may include any number of modifications to the fluid, but of most relevance here, the removal of unwanted contaminants by filtration methods, chemical treatment, or irradiation.
Types of contaminants that can be removed or rendered inactive in these processing steps can include:                1. Live biological matter, such as bacteria, viruses, protozoa, molds, etc. which might cause disease or stimulate allergies,        2. Dead biological matter, such as hair, dust, dander, excrements, and germs previously deactivated, etc. which might aggravate allergies or cause respiratory or digestive problems.        3. Organic compounds, such as from building materials, plant exhausts, drying paints, pesticides, industrial chemicals, human and animal wastes, etc.        4. Inorganic compounds such as metals, minerals, nitrates, phosphates, sulfates, etc. which are byproducts of industrial processing or fluid handling.        5. Pharmaceutical byproducts that remain in the fluid stream after municipal water treatment, and        6. Treatment byproducts from ozonation and chlorination, residuals of which may remain in the fluid stream after fluid (e.g., water) treatment.        
No purification technology is effective at removing all of the undesired contaminants. For instance, air filtering in HVAC systems, even HEPA filtering, cannot remove all viruses and bacteria from a fluid stream and often accelerate their reproduction. As a result, most buildings in the world do not have adequate systems for treating indoor air quality. Similarly, filtration and chlorination methods are commonly combined for municipal water quality at the source, but these often do not address heavy metals, pharmaceutical byproducts, dissolved organic compounds, a growing list of germs, and such that is collected in the downstream water distribution system. Furthermore, any failures in maintenance of the chemicals and filters can worsen the water quality.
Additionally, existing technologies can create toxic waste streams in addition to the fluids they purify. Reverse osmosis, for instance, typically produces an output stream of more pure water and a second efflux stream that is more contaminated than the input fluid stream. Filtration technologies accumulate toxins and provide accelerated breeding grounds for germs, creating a toxic waste that must be treated, stored or it will become an environmental pollutant. Chlorination, ozonation, and other chemical methods can add chemicals into the fluid stream and result in byproducts of the chemical additives.
Ultraviolet light, especially deep UV light at wavelengths less than 300 nm, has been shown to be effective in disrupting the DNA of some germs and other organisms, rendering them unable to reproduce (sterilization), which can halt the spread of disease. Such deep UV light treatment deposits no chemicals in a fluid stream and in fact can also break down some contaminants in the fluid stream as well, either directly, indirectly through the generation of ozone or, if intensities are high enough, through photo-disassociation or photolysis. However, UV light treatment does not completely kill germs, nor remove organic waste or most other contaminants from the fluid stream unless very high intensities or very low wavelengths are used, which is often practically prohibitive. Typically used downstream of filtering technology, UV Germicidal Irradiation (UVGI) at 253.7 nm using low pressure mercury lamps is the fastest growing and best documented UV technique with accepted standards in place by many governing bodies. Low pressure Hg lamps are also efficient at generating almost all of their light at 253.7 nm, with wall-plug energy conversion efficiency up to >35%. Medium and high pressure mercury lamps and Xenon lamps can also be used to create higher intensities, although typically at the cost of reduced efficiency and lamp life.
An additional known UV technology, semiconductor photocatalysis, results when a suitable semiconductor material is irradiated by a light source with photon energies greater than its band gap (wavelengths less than the band gap wavelength) in the presence of moisture. These photons excite the semiconductor material to facilitate production of hydroxyl ions and other active species in the fluid at the semiconductor surface that break down certain organic materials through powerful oxidation and reduction reactions while leaving the semiconductor unchanged in the process. Nearly 1000 materials have been reported as successfully photocatalyzed in this way, mostly using anatase crystals of TiO2, sometimes modified for increased photoreactivity.
However, there are many drawbacks that have restricted the use of semiconductor photocatalysis in purification applications, including relatively poor photon efficiency, long contact times, saturation of the surface with contaminants, and the practical issues of supplying a high surface area of photocatalyst into a fluid with uniform optical illumination at a suitable wavelength.
Therefore, a need exists for improvements in fluid purification technology.